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Monarch butterflies -- one of the sure signs of spring and summer -- may not be as plentiful this year across the USA, in part because of the ongoing drought and recent wildfires in Texas that ravaged their food sources.

The butterflies usually fly north across Texas this time of year, as they migrate from Mexico into the USA. In 2012, Texas endured its hottest year on record, according to the National Climatic Data Center. This came on the heels of the state's driest year on record in 2011.

"The severe drought in Texas and much of the Southwest continues to wreak havoc with the number of monarchs," says butterfly tracker Craig Wilson, a senior research associate at Texas A&M University.

The lack of rain and raging fires diminished the main food source for butterfly larvae (milkweed) and also decreased food sources for adult butterflies (such as wildflower nectar), Wilson says.

No single monarch butterfly ever completes its migration from Mexico to as far north as Canada and back each year, according to National Geographic. Instead, generations of monarchs make this journey -- born into a relay race no one butterfly finishes.

Reports from Mexico -- where the monarchs have their winter breeding grounds -- show their numbers are significantly down, a trend that's been ongoing for much of the past decade.

"The conditions have been dry both here and in Mexico in recent years," reports Wilson. "It takes four generations of the insects to make it all of the way up to Canada, and because of lack of milkweed along the way, a lot of them just don't make it."

Milkweed mainly grows in the wild, and changing farming practices have greatly reduced its growth, according to Wilson. For instance, increased use of herbicides is adversely affecting milkweed.

"But if people want to help, they can pick up some milkweed plants right now at local farmer's cooperative stores," Wilson says, "and this would no doubt be a big boost to help in their migration journey.

"It is important to have a national priority of planting milkweed to assure there will be monarchs in the future," Wilson believes. "If we could get several states to collaborate, we might be able to provide a 'feeding' corridor right up to Canada for the monarchs."